Micromagnetic Simulation Insights into the Coexistence of Neel and Bloch Skyrmions in [Pt/Co/Cu]_N Multilayers

Magnetic skyrmions are one of the most promising candidates for next-generation information storage due to their small sizes, thermal stability, and high energy efficiency. Recently we have discovered magnetic skyrmions in epitaxial [Pt/Co/Cu]_N multilayers using magnetic force microscopy (MFM) and Lorentz transmission electron microscopy (LTEM) [1]. In our LTEM experiments on the devices patterned from [Pt/Co/Cu]₅ multilayers, we have found that the Bloch and Neel skyrmions can coexist upon applying current pulses. To understand this behavior, we have performed micromagnetic simulations in which [Pt/Co/Cu]_N multilayers are modeled as a stack of 3*N layers. With this micromagnetic model, we are able to reproduce several major experimental observations: (1). Out-of-plane single domain to multidomain transition between N = 4 to N = 5. (2). The diameter of skyrmions in [Pt/Co/Cu]₅ multilayers, which is ~120 nm. (3). The inherent coexistence of Neel and Bloch skyrmions that undergoes a transition with applied pulse current.